This invention relates to opioid-containing pharmaceutical compositions which are useful in effecting transdermal delivery of a therapeutic dose of the opioid to the systemic ciruclation of a mammal.
Many opioids are known to have poor bioavailability in the mammalian systemic circulation due to extensive initial metabolism of the drug by the liver and intestines. Furthermore, the bioavailability of orally administered opioids may be unpredictable since various factors such as changes in acidity and food content can cause changes in the amount of drug absorbed from the gastrointestinal tract. Also, oral administration does not necessarily insure good patient compliance.
Parenteral administration of opioids provides better bioavailability than oral administration. However, the various routes of parenteral administration such as intravenous, intramuscular, and subcutaneous delivery are not convenient for chronic therapy. This is particularly true for those opioids which exhibit short biological activity half-lives.
Topical formulations of opioids do not necessarily provide delivery of a therapeutic dose of the drug to the systemic circulation and thus provide poor or unpredictable bioavailability.
Transdermal delivery of opioid drugs to the mammalian systemic circulation would be an alternative mode of administration which could provide the following advantages:
1. Improved and predictable bioavailability of the opioid as compared to oral administration since transdermal delivery avoids initial metabolism by the liver and intestines, and unpredictable absorption from the gastrointestinal tract.
2. A stable blood serum level of the drug resulting in a prolonged pharmacological effect similar to intravenous infusion.
3. Easily adjustable dosing rate which provides maximization of efficacy and minimization of side effects.
4. Easily removable drug source which provides rapid cessation of dosing and elimination of the drug from the body fluids.
5. Convenience of dosing which provides improved patient comfort as compared to parenteral administration and the possibility of greater patient compliance as compared to oral administration.
Transdermal drug delivery is distinguished from topical drug delivery by the fact that while a transdermal formulation is specifically designed to provide a predictable and therapeutically significant rate of delivery of the drug to the systemic circulation, a topical formulation is specifically designed to provide a therapeutic effect only to the local area to which the drug is applied. Furthermore, topical formulations are often designed to prevent any systemic delivery of the drug in order to minimize side-effects. However, even if the topical delivery of a drug does result in systemic absorption, the amount of drug delivery to the circulation is variable and uncontrolled.
The skin is an excellent barrier to the penetration of many foreign substances. The feasibility of using transdermal delivery of opioid drugs as a route of administration requires that a therapeutic rate of drug delivery through the skin be achieved. This can be accomplished if the skin can be made more permeable to the drug.
Factors which determine the permeability of the skin to a particular drug include drug diffusivity through the skin membrane, vehicle/skin drug partitioning, and drug concentration in the vehicle. In addition, certain materials used as adjuvants in vehicles may affect the characteristics of the skin membrane barrier and thus alter the permeability of the skin to the drug. Such materials are referred to as skin penetration enhancers. These penetration enhancers are important in the optimization of transdermal drug delivery because of the necessity for maximization of penetration rates and minimization of lag times in the drug penetration through the skin.
The permeability of the skin to a drug is influenced by a combination of physico-chemical parameters for both the drug and the vehicle, as discussed above. Thus, effective transdermal delivery of a particular class of drugs requires the selection of an appropriate vehicle. The optimum vehicle for one class of drugs may not be effective for transdermal delivery of another class of drugs since the properties of the vehicle and the drug must be matched to insure a therapeutic rate of drug delivery through the skin.
Ritter et al., U.S. Pat. No. 3,867,528, issued Feb. 18, 1975, disclose pharmaceutical compositions comprising ethoxylated stearyl alcohol and steroids which provide greater penetration of the steriod through the skin to produce greater topical therapeutic activity. The disclosed composition is shown to provide greater penetration of the steroid than other topical formulations, but there is no indication as to which ingredient in the disclosed formulation contributed to the enhanced penetration. There is no disclosure that stearyl alcohol is effective in producing transdermal delivery of a therapeutic dose of an opioid to the systemic circulation.
Katz et al., U.S. Pat. No. 3,592,930, issued July 13, 1971; Katz et al., U.S. Pat. No. 3,888,995, issued June 10, 1975; and Chang et al., U.S. Pat. No. 3,924,004, issued Dec. 2, 1975, disclose pharmaceutical compositions comprising corticoids and from 5 to 40 percent saturated fatty alcohol having from 16 to 24 carbons. The alcohol is used as a vehicle for the topical administration of the anti-inflammatory corticoid. There is no disclosure that the fatty alcohol is effective in producing transdermal delivery of a therapeutic dose of the steroid to the systemic circulation, or that the alcohol would make the skin more permeable to opioids.
Magid et al., U.S. Pat. No. 3,275,510, issued Sept. 27, 1966, disclose topical antitussive formulations comprising a mixture of an orally active antitussive agent and a lipophilic or hydrophilic carrier. The disclosed antitussive agents include codeine, dihydrocodeinone, 1-.alpha.,2-methyl-8-methoxy-6,7-methylenedioxy-1-(6,7-dimethoxy-3-phthali dyl)-1,2,3,4-tetrahydroisoquinolone, .alpha.-(dimethylaminoethyl)-o-chlorobenzhydrol, d-3-methoxy-N-methylmorphinan and medically acceptable acid addition salts thereof. There is no disclosure or suggestion that the disclosed formulations contain any particular penetration enhancer(s), that the rate of systemic delivery of the antitussive agents can be controlled, that the disclosed formulations would be useful for compounds which are not orally active, or that the disclosed formulations would be effective for any indication other than as antitussives.
Sipos, U.S. Pat. No. 4,091,090, issued May 23, 1978, discloses topical anesthetic compositions wherein there is obtained an enhancement of the activity of the topical anesthetic agent by combining the anesthetic agent with an effective amount of a penetrant accelerator cyclohexyl alkanol. The compositions are shown to exhibit quicker onset and deeper anesthesia at the site of application. The effect, however, is still a local anesthesia and there is no disclosure that these alcohols effect systemic delivery of the anesthetic or that these alcohols or fatty alcohols and fatty acids would be effective in producing transdermal delivery of a therapeutic dose of an opioid.
Luedders, U.S. Pat. No. 4,299,826, issued Nov. 10, 1981, discloses topically applied, anti-acne pharmaceutical compositions which comprise an erythromycin compound and a pharmaceutically acceptable penetrating carrier wherein said carrier comprises a penetration enhancing amount of diisopropyl sebacate and a dermatologically acceptable alcohol. There is no disclosure or suggestion that the carrier components would make the skin more permeable to opioids.
Rajadhyaksha, U.S. Pat. No. 4,405,616, issued Sept. 20, 1983, discloses a method for administering systemically active agents including analgesics, analgesic combinations, and anorexics, through the skin in a transdermal device or formulation. The skin penetration enhancers, disclosed as achieving transdermal delivery of the systemically active agents, are lactams such as 1-dodecylazacycloheptan-2-one. The utility of fatty acids or fatty alcohols as penetration enhancers for opioids is not disclosed or suggested.
Bernstein, U.S. Pat. No. 4,416,886 (Bernstein), issued Nov. 22, 1983, discloses a method for treating severe pruritis which comprises the topical administration of a solution, lotion, cream or ointment comprising naloxone or naltrexone. The patent discloses that the liquid dosage forms for the topical administration of naloxone or naltrexone comprise volatile diluents such as alcohol and glycol. There is no disclosure or suggestion that the alcohol or glycol is effective in producing transdermal delivery of a therapeutic dose of naloxone or naltrexone to the systemic circulation. There is also no disclosure or suggestion that even an appreciable amount of naloxone or naltrexone is delivered to the systemic circulation since the antipruritic effect is a local effect.
Michael A. Stillman et al., Relative irritancy of free fatty acids of different chain length, Contact Dermatitis, 1, 65-69 (1975), found that the most irritating fatty acids to human skin were C.sub.8 to C.sub.12.
There is a need for opioid-containing vehicles which are effective in the transdermal delivery of a therapeutic dose of the drug to the mammalian systemic circulation. The opioid-containing pharmaceutical compositions of the instant invention fulfill this need.